From a flowing fluid having potential energy (pressure head) and kinetic energy (velocity head) energy may be extracted and may be converted by a turbine to mechanical energy, such as rotational energy, using a turbine. The extracted rotational energy may for example be used to drive a generator to generate electric energy.
Gas turbines comprise a compressor for compressing air which is then mixed with fuel and burned in a combustion chamber. The hot combustion gases are then expanded through a turbine providing a mechanical energy that can be used to drive an external apparatus, such as a electrical generator, a compressor or a pump.
Compressors may also be used to compress a gas to be used in industrial processes or to pump natural gas in a pipeline.
The compressor comprises a rotor shaft which is rotatably supported within a casing. Within the casing, the rotor shaft typically is supported by a bearing comprising plural pad bearings. Plural rotor blades are connected to the rotor shaft and extend radially outwards from the rotor shaft. The rotor shaft rotates around a rotation axis oriented in an axial direction driven by the mechanical energy provided to the compressor, for example by a turbine further downstream sharing the shaft with the compressor. The rotation of the rotor shaft drives the gas through the compressor towards a higher pressure. At a particular axial position along the rotation axis plural rotor blades may be connected to the rotor shaft forming a row of rotor blades. Plural rows of rotor blades may be connected to the rotor shaft at axial positions spaced apart from each other.
For appropriately guiding the streaming gas to the rotor blades a row of guide vanes is arranged downstream of a row of rotor blades, wherein the guide vanes are fixedly connected to the casing of the compressor. Thereby, the casing belongs to the stator part of the compressor. Thus, the guide vanes remain at rest, while the rotor blades rotate relative to the guide vanes and also relative to the casing. Further, the compressor may comprise a row of inlet guide vanes upstream the first row of rotor blades.
The guide vanes extend radially inwards towards the rotating rotor shaft. Thereby, a gap is formed between a radially inner end of the guide vanes and the rotor shaft. The streaming gas delivered by the rotor blade impinges onto an upstream or pressure surface, typically concave surface, of the guide vane and flows along the upstream surface and also along a downstream or suction surface of the guide vane to be directed to a rotor blade, respectively a row of rotor blades, downstream the guide vane, respectively the row of guide vanes. Since the pressure of the impinging gas is higher at the upstream surface of the guide vane than at the downstream surface of the guide vane, the upstream side of the guide vane is also called pressure side of the guide vane and the downstream side of the guide vane is also called the suction side of the guide vane. Because of the pressure difference between the pressure side and the suction side of the guide vane the impinging gas partially flows through the gap between the radially inner end of the guide vane and the rotor shaft from the pressure side of the guide vane to the suction side of the guide vane, thereby impairing the efficiency of the compressor.
In order to diminish the flow of the streaming gas from the pressure side to the suction side of the guide vane, the gap between the radially inner end of the guide vane and the rotor shaft has to be constructed as small as possible. However, due to thermal expansion during operation of the compressor which expansion is different for different components of the compressor, the gap may not be constructed too small. Instead, a particular running clearance between the radially inner end of the guide vane and the rotor shaft must be maintained.
From the document US 2008/0213098 A1 a blade for a turbo machine is known, wherein the blade has a blade tip which is curved in relation to the blade airfoil profile.
From the document GB 710938 a rotor blade for an axial flow fluid machine is known, wherein a stiffened plate is provided at a tip of the rotor blade.
From the document GB 1 491 556 a rotor blade for turbo machines is known, wherein the blade carries a tip plate which projects therefrom on the leading and/or trailing side.
From the document GB 733,918 a blade of elastic fluid turbines is known, wherein a small plate is fastened onto the top surface of the blade tip.